The manufacture of nonwoven fabrics is a highly developed art. Generally, nonwoven webs or mats are made by forming filaments or fibers of varying or specific diameter and depositing them on a carrier in such a manner so as to cause the filaments or fibers to overlap or entangle as a web of a desired basis weight.
Various means have been developed in an attempt to control the form of the processed fibers which in turn affects the properties of the formed web. For example, U.S. Pat. No. 2,571,457 to Ladisch, issued Oct. 16, 1951 discloses a spray nozzle for forming filaments and/or fibers in diameters of about one micron and smaller by passing a polymer stream through the central orifice of a nozzle with an elastic fluid such as air being caused to spiral towards the vertex of a cone. U.S. Pat. No. 3,017,664 to Ladisch, issued Jan. 23, 1962 discloses a fiber forming nozzle wherein a stream of polymer material exits a nozzle orifice in the form of a tube, formation of the tube being caused by the spreading of the polymer over the outside wall of a circular body positioned in the orifice. An elastic fluid rotating in a spiraling manner around the film of polymer with a very high velocity creates a vacuum between the film and elastic fluid. Fibers are picked up from the film of fiber forming liquid and drawn out to fineness in the elastic fluid. Although both Ladisch patents disclose a spiraling air which surrounds the resin flow from an orifice, the emitted air is transmitted through nozzle openings which do not surround the polymer stream.
U.S. Pat. No. 3,543,332 to Wagner et al, issued Dec. 1, 1970, discloses the production of fibers utilizing a spinning nozzle, the spinning nozzle having a central orifice for forming a polymer stream and additional orifices surrounding the central orifice for the passage of fiber forming air.
U.S. Pat. No. 3,755,527 to Keller et al, issued Aug. 28, 1973, discloses a process for producing meltblown nonwoven synthetic polymer mats. The meltblown process utilizes a plurality of extrusion orifices through which a melted polymer resin is extruded. On each side of the plurality of orifices is a hot air slot for supplying a stream of hot gas in the form of a sheet on each side of the plurality of fiber streams formed from the resin. To produce fibers having diameters between 10 and 40 microns, combinations of die tip temperature, resin flow rate, and resin molecular weight are selected to give an apparent viscosity in the die holes from about 10 to 800 poise. The viscosity is then adjusted into an operable range by varying the die tip temperature.
U.S. Pat. No. 3,905,734 to Blair, issued Sep. 16, 1975 discloses improvements for an apparatus for continuous tube forming by meltblowing techniques. The assembly utilizes knife-like streams of forming gas on each sideof a polymer exit orifice.
U.S. Pat. No. 3,978,185 to Buntin et al, issued Aug. 31, 1976 discloses a meltblown nonwoven mat prepared from thermoplastic polymer fibers which are alleged to be substantially completely free of polymer shot and produced at a high polymer throughput rate in a specific meltblowing process in which thermoplastic polymer resins having a specific viscosity range are degraded in the presence of a free radical source compound.
U.S. Pat. Nos. to Oshido et al, 4,135,903 issued Jan. 23, 1979 and 4,185,981 issued Jan. 29, 1980 disclose a method and apparatus for producing fibers from a heat softening material utilizing high speed gas streams which cause the melted polymer to rotate around its central axis line and transform it into a substantially conical shape whose cross-section gradually decreases towards its flowing direction in a first cone and is caused to advance in the form of fiber from the tip of the cone in the flowing direction and outwardly in the radial direction in a second cone.
It remains desirable to develop further apparatus and method for forming fibers from molten fiber forming resins and then forming mats from the formed fibers wherein the apparatus and process provide increased throughput on a per-hole basis and wider operating ranges.
The above references teach apparatus and processes which are quite capable of forming flat mats or webs of nonwoven material which are most commonly subjected to additional processing for incorporation into other products such as diapers and other personal care items or subsequent conversion into such items as disposable workwear. With the advancement of nonwoven fiber forming technology, the uses and applications for such materials have been greatly enhanced. As new uses and applications are found, the design limitations of current equipment become more evident. With the increasing costs of the polymers used in the formation of fibers, overall production costs become an ever important factor. One way to reduce the cost of the nonwoven material is to increase the production capability of the equipment. Unfortunately, with current meltblowing equipment, there are severe limitations as to the amount of polymer throughput which can be tolerated by the meltblowing dies. As polymer viscosities and pressures increase, so does the likelihood of the dies, themselves, fracturing or "zippering" as it is known in the industry. It is therefore an object of the present invention to provide an apparatus and process which allow for substantially higher polymer pressures and thus higher throughputs on a per-hole basis relative to normal meltblown die tip construction.
Another major problem in the formation of nonwoven fibers and the resultant webs is a phenomenon called "shot". Shot occurs when drawing air is improperly applied to the extruded polymer stream. When this condition occurs, small beads of polymer are formed along with the fibers, thereby giving the formed web a very rough feel. This can be caused by equipment design, improper adjustment of the air to polymer ratio, processing conditions, or a combination of the three. In almost all applications, shot is not desirable. It is therefore an object of the present invention to provide a process and apparatus with increased air flow to and around the extruded polymer, when desired, to decrease shot, and increase fiber formation efficiency or reverse the process when necessary.
As the demands upon nonwoven materials become more complex, it is sometimes desirable to form nonwoven materials which are comprised of intimately entangled fibers of different polymer composition and/or fiber size. The actual generation of materials using more than one polymer and/or fiber typically requires production in a multi-bank layered setup wherein one bank of dies forms fibers of one size or polymer, while another set of dies produces fibers of another size or polymer. It is therefore an object of the present invention to provide an apparatus and process which will permit the formation of multi-component nonwoven materials in a more localized and efficient manner.
Another drawback with current meltblowing apparatus and processes are their inability to produce nonwoven materials which are three-dimensional in structure and/or zoned in density in either or both the machine and cross directions. A primary reason for this is the fact that the meltblowing equipment as described above is planar in design and must operate on a continuous basis due to the heating requirements of the polymer and the problem with die holes plugging with stagnant polymer. Consequently, such equipment cannot be cycled on and off to create nonwoven materials having varying densities and other attributes. It is therefore an object of the present invention to provide an apparatus and process which will allow cyclical release of polymer during the fiber forming process.
With current meltblowing equipment, production runs are made at a specified width which usually corresponds to the width of the bank of meltblown die tips or openings. To change widths, holes must be plugged or the system shut down to refit the line with smaller or larger banks of die tips. It is therefore an object of the present invention to provide an apparatus and process which allow on-line variations in production widths of the nonwoven material. Lastly, current meltblowing equipment often becomes clogged when the small die openings become filled with solidified polymer. Usually, there is very little that can be done to unclog the holes while the machinery is running. While a few clogged holes will usually not affect production quality, once enough of the holes become clogged, the die tip must be taken off-line and cleaned--a costly and time-consuming process. It is therefore yet another object of the present invention to provide a process and apparatus which is self-cleaning.
These and other objects and advantages of the present invention will become more apparent upon a further review of the following specification, drawings and claims.